In elevator systems steel cables have conventionally been employed as the suspension means for purposes of suspending and/or driving an elevator car. In accordance with a further development of such steel cables, belt-type suspension means are also employed, which have tension load carrying members and a jacketing arranged about the tension load carrying members. However, such belt-type suspension means cannot be monitored by conventional means, because the tension load carrying members, which determine the fracture load of the suspension means, are not visible through the jacketing.
For purposes of monitoring such tension load carrying members in belt-type suspension means a test current can be applied onto the tension load carrying members. In the current circuit thus established, or in the plurality of current circuits thus established, a current flow or current strength, a voltage, an electrical resistance, or an electrical conductivity, are measured. On the basis of such a measured quantity conclusions can be drawn regarding the integrity, that is to say, the degree of wear, of the suspension means. If, for example, the diameter of a tension load carrying member is reduced as a result of breakages of individual wires, or by metallic wear, the electrical resistance of the said tension load carrying member increases.
U.S. Pat. No. 7,123,030 B2 discloses such a method for determining the degree of wear of a belt-type suspension means. On the basis of a specific electrical resistance of the electrically conducting tension load carrying members a breaking force is defined for the suspension means.
However, in such a monitoring method, as described in the prior art, only a general statement can be made concerning the state of a suspension means. Here interference factors such as temperature variations, electromagnetic radiation, movements of the means suspension, and similar, which have a direct influence on the electrical resistance of the tension load carrying member, are not sufficiently taken into account.